Piezoelectric pressure and temperature sensors typically have a crystal resonator located inside a housing with electrodes. Environmental pressure and temperature are transmitted to the resonator, via the housing, and changes in the resonator are sensed and used to interpret the pressure and/or temperature. U.S. Pat. No. 3,617,780 describes one example of a piezoelectric pressure transducer. In conventional devices, known as single-mode transducers that utilize single-mode oscillation, the resonator is affected by both temperature and pressure such that some devices may not be suitable for use in environments where both temperature and pressure vary.
One approach that is utilized to minimize fluctuations in pressure measurements is to use resonators with dual-mode oscillation. U.S. Pat. Nos. 4,419,600, 4,547,691 and 5,394,345 disclose examples of such pressure transducers. However, transducer geometry for such resonators tends to be relatively more complex, and the transducer tends to be larger due to the manufacturing process. Under certain conditions, such as in oil or gas wells, stress on the transducer may cause material twinning or micro-cracks that might damage the pressure transducer.
Pressure transducers using thickness shear vibrations typically utilize the aforementioned single-mode oscillation. In such cases, although the geometry of single-mode transducers may be simpler than dual-mode transducers, such transducers provide only pressure data. In this, temperature data has to be obtained from a separate temperature sensing device, preferably located close to the transducer, which makes the temperature compensation process relatively slower with potential inaccuracies.
As will become apparent from the following description and discussion, the present invention overcomes at least some of these deficiencies and provides an improved pressure transducer.